Conventionally, conjugated diene polymers are widely used in footwear, modification of plastics, asphalt, viscous adhesion field, and the like.
In the production of a conjugated diene polymer, a monomer is polymerized in a hydrocarbon solvent inert to a catalyst, and a conjugated diene polymer produced is obtained in a state uniformly dissolved or in a state suspended in the solvent. Therefore, in order to recover the conjugated diene polymer, a step of separating the conjugated diene polymer and the solvent is required.
Examples of the method of separating a conjugated diene polymer and a solvent include a steam stripping method and a direct solvent removal method. A direct solvent removal method in which a solvent is removed from a polymer solution in a vent extruder to recover a conjugated diene polymer has been proposed as an advantageous method in terms of economical efficiency (for example, refer to Patent Literature 1, 2).
However, a molded article prepared by molding the conjugated diene polymer obtained by the direct solvent removal method still has a point that should be improved in terms of quality. Therefore, in terms of economical efficiency and quality, there is required a method different from the steam stripping method which provides relatively good quality but is poorer than the direct solvent removal method in terms of economical efficiency.
Conventionally, following methods have been proposed to the above requirement.
Patent Literature 3 proposes a method including deactivating an active terminal after polymerization and then adding two types of phenolic compounds.
Patent Literature 4 proposes a method including deactivating an active terminal after polymerization, adjusting the pH of a polymer solution, adding a phenolic stabilizer, removing a solvent with a screw having a vent zone, and further adding a phosphorus stabilizer.
Patent Literature 5 proposes a method including deactivating an active terminal after polymerization, adding a carbon oxide gas to a polymer solution and neutralizing a catalyst residue in a step of continuously transferring the polymer solution to a solvent removing step.
Patent Literature 6 proposes a method including adding an antioxidant and an optional terminator after polymerization, adjusting the solution concentration to 76.9 mass % or more (the amount of a residual solvent to 30 parts by mass or less based on 100 parts by mass of a polymer), and then adding a carbon oxide gas in the state where the water content is adjusted to 0.5 mass % or less.